In manufacturing a metal mold as a base technique in a manufacturing industry, high speed and high quality machining using a machining tool having a high reliability is particularly desired. In metal mold machining, rough cutting is a first process to shape a workpiece into a desired form. The total volume of material which is cut off by rough cutting is very large. Therefore, an extremely high machining efficiency is required in rough cutting. In addition, a machining precision such as surface roughness or surface shape is required in the final product. In order to reduce the whole process time, not only the process time required for rough machining and finish machining is reduced but also a reduction of a set-up time which is needed as part of those processes is important.
As a rough cutting tool for manufacturing the metal mold, a cutting tool such as ball end mill or milling cutter has been widely used. Although the cutting tool can perform efficient rough machining, the shape of the end of the tool is changed due to wear and it is difficult to compensate for this change, so that there is a problem that the machining precision such as surface roughness or surface shape is low.
As a finishing tool for manufacturing the metal mold, a grinding tool using a grinding wheel has been widely used. As for the grinding tool, however, it is difficult to efficiently and stably grind a ductile material such as aluminum, copper, or plastic due to clogging of the grinding surface.
Further, in the case of rough cutting by a rough cutting tool and finishing by a finishing tool, a detachment and a re-attachment of the tool or workpiece is indispensable, so that there is a problem that an occurrence of attachment error cannot be avoided.
In association with a development of the recent technology, desire for ultraprecise machining has rapidly and highly advanced. As electrolytic grinding means which satisfies the above desire, the electrolytic in-process dressing (ELID) grinding method has been developed and proposed by the same applicant as the present invention ("Trend of Latest Technique of Mirror-grinding" in RIKEN Symposium held on the fifth of March, 1992).
The ELID grinding method is a method in which a conductive grinding wheel is used in place of an electrode in the conventional electrolytic grinding, an electrode which faces the grinding wheel at a distance is provided, a voltage is applied between the grinding wheel and the electrode while a conductive liquid is supplied between the grinding wheel and the electrode, and the workpiece is ground by the grinding wheel while dressing the grinding wheel with electrolysis. In the ELID grinding method, even when abrasive grain are fine, no clogging of the grinding wheel occurs by dressing the abrasive grains with electrolytic dressing. Consequently, by using abrasive fine grains, a very excellent surface like a mirror surface can be obtained with ELID grinding. Therefore, it is expected that the ELID grinding method, when applied to various grinding jobs can maintain the cutting ability of the grinding wheel from highly efficient grinding to mirror surface grinding and can form a highly accurate shape in a short time, which cannot be realized by the prior art.
In the ELID grinding method, although it is possible to grind at a high efficiency without clogging of the grinding wheel, it is difficult to eliminate chips with respect to relatively soft, ductile material such as aluminum, copper, or plastic, because such materials cannot be deeply cut. Therefore, there is a problem that the machining efficiency is lower than that as a conventional cutting tool such as a ball end mill or milling cutter.